Technical Field
The present subject matter relates to an apparatus and a method for determining a characteristic feature of a vehicle travelling on a roadway. The present subject matter further relates to a system comprising at least two such apparatuses.
Background Art
The determination of characteristic features of vehicles is important for many tasks in the field of traffic control, traffic monitoring and traffic billing. Individual vehicles can thus be detected and, for example, counted or automatically tracked, assigned on the basis of their features to certain vehicles classes, for example, passenger vehicles or lorries, and class-dependent tariff models or vehicle-class-dependent driving restrictions in road toll systems or parking fee systems can be created, checked and implemented on this basis.
Predominantly optical systems, such as light barriers, laser scanners or video cameras, are currently used to determine characteristic features. For example, a laser scanner operating on the basis of the light-section method is known, for example, from EP 2 306 429 B1. Such systems are reliant on good visibility and are therefore highly dependent on the weather; they often fail in rain, snow or spray. The optics of light barriers, laser scanners (e.g. US 2002/0140924 A1) and video cameras also require frequent cleaning in order to remain ready for use.
In sub-areas, such as traffic flow monitor systems, radar systems are also currently used, which, from a raised point, for example an antenna mast next to a motorway, detect the movements of the traffic by means of Doppler radar and can track said movements in a radar image. The measurement accuracy of such radar systems is limited however, and the evaluation of the speeds requires a high computing effort in order to create the traffic flow image. In document EP 0 636 900, radio waves are used for velocity and distance measurements to therefrom create a distance measurement point silhouette of the vehicle.